Revert "Add backtrace to error function"

This reverts commit 5b518ed2fe.

This caused duplicate tracebacks and tracebacks when unwanted.
It also ignored the level argument to error() and didn't pass the message (or level) to debug.traceback().
Use xpcall() or lua_pcall()'s errorhandler argument instead.

builtin/builtin.lua

@@ -10,12 +10,6 @@ print = minetest.debug
 math.randomseed(os.time())
 os.setlocale("C", "numeric")
 
-local errorfct = error
-error = function(text)
-	print(debug.traceback(""))
-	errorfct(text)
-end
-
 -- Load other files
 local modpath = minetest.get_modpath("__builtin")
 dofile(modpath.."/serialize.lua")

builtin/mainmenu.lua

@@ -2,12 +2,6 @@ print = engine.debug
 math.randomseed(os.time())
 os.setlocale("C", "numeric")
 
-local errorfct = error
-error = function(text)
-	print(debug.traceback(""))
-	errorfct(text)
-end
-
 local scriptpath = engine.get_scriptdir()
 
 mt_color_grey  = "#AAAAAA"